In the smelting and production of liquid iron, the ironmaking system normally consists of iron oxide and a carbonaceous fuel processed by hot air or oxygen blowing at elevated temperatures. The carbon from the fuel forms carbon monoxide (CO) which serves as the reductant for the iron oxide. In addition, the carbonaceous fuel supplies elemental carbon with is soluble in the liquid iron and is commonly the source of sulfur in the reduction system. This sulfur, during ironmaking, is generally in the gaseous form of hydrogen sulfide (H.sub.2 S) with minor amounts of carbonyl sulfide (COS). These gaseous forms of sulfur are highly soluble in the liquid iron. At ironmaking temperatures of 1500.degree. C., up to 36.5% of the sulfur by weight is soluble in the liquid iron with a series of liquid solutions from pure iron to a composition higher in sulfur than iron sulfide (FeS). In these compositions of iron sulfide there is a eutectic composition at 31% sulfur having a melting temperature of 988.degree. C. Therefore throughout the smelting process, conducted above the eutectic temperature level, hot metallic or liquid iron has a high affinity for and is a strong absorber of gaseous sulfur.
Any appreciable level of sulfur in the liquid iron typically destroys the malleable metallic properties of the solidified iron for subsequent forming and utilization. In fact, a sulfur content of as little as 0.1% in the liquid iron can ruin the iron for subsequent refining, casting and steelmaking. With high gaseous sulfur concentrations emanating from the carbonaceous fuel in the liquid iron-reducing gas system, the sulfur content of the iron can easily exceed the 0.1% sulfur limit, and are often found to exceed 1.0% in the liquid iron.
Without control of sulfur in the liquid iron, high concentrations of sulfur in the reducing gases cannot be tolerated, thus limiting the ironmaking process to low sulfur iron ores and low sulfur fuels. Therefore what is needed is a method of maintaining the desired low sulfur levels in the liquid iron even in the presence of high sulfur gases, thereby enabling the production of liquid iron utilizing high sulfur carbonaceous fuels (i.e., petroleum coke, low ash high sulfur coals). The present invention provides such a method.